The objective of these studies is to delineate the molecular mechanism by which the phosphorylation state of skeletal muscle glycogen synthase is altered in diabetes and by insulin treatment. Emphasis will be focused on those protein kinases which phosphorylate sites 2 and 3 in glycogen synthase and/or activate the Mg++/ATP-dependent protein phosphatase I. Effects of the insulin receptor tyrosine protein kinase on these serine/threonine protein kinases and phosphatases will be examined directly using purified enzymes as well as in situ in diaphragm and cultured cells. In the latter case a highly specific antiphosphotyrosine monoclonal antibody affinity column will be utilized to selectively purify protein kinases and phosphatases containing phosphotyrosine. Another approach will be to assess potential effects of insulin-generated "modulator" molecules, derived from a phosphatidylinositol-glycan by activation of a specific phospholipase C, on these glycogen synthase protein kinases and phosphatases. Potential effects of insulin on the subcellular distribution of the protein kinase that activates the Mg /ATP- dependent phosphatase and on the phosphatase itself will be examined.